Not sure how they got through, since all users are set to moderate when joining. Join dates on all the offenders were April 17th and 18th, but I did not approve any members either day. Gonna have to look at the settings for people waiting for approval.
edited: Looked at all the settings and they appear to be correct, anybody waiting for approval cannot post. However, I did a search of members who have joined since 04/01/2013 and there are 38 registered users. There is no way I approved 38 people in the since then, so some how they are getting through or someone else is approving members.